Galvanic Corrosion Considerations
When using stainless steel for anchors and structural connections such as steel plates, is it always assumed to be a passive stainless steel, such as SS316 or SS304?
Additionally, when stainless steel is combined with anodic metals like aluminum, would it be more prone to galvanic corrosion compared to copper, given their relative positions in the galvanic series?
Finally, if a question does not specify whether the stainless steel is in a passive or active state, should it be assumed to be passive by default?
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NCARB, if you are monitoring this….this is a really important question to answer…my experience tells me that the exams do not specify passive vs active stainless and that’s super important to know in the context of metal corrosion…(another reason that volunteer architects should not be making these technical questions unless they are also run by subject matter experts, who would have flagged this issue years ago).
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All,
Michael asked me to follow up on this one - it's really pretty simple, and there's a fairly good reason stainless steels wouldn't be identified as passive or active on the exam.
While I'm sure there are specific recipes of stainless steels that are generally more active or generally more passive, all stainless steels are passive unless the environment they are in makes them active. Stainless steel is passive when there is enough oxygen in the environment for the chromium and other elements in the steel to form a protective oxide layer on the surface of the steel. Stainless steels become activated (read: the oxide layer fails and the steel starts to rust) when the surface of the steel is in an environment with too little oxygen for the protective oxide layer to form or to heal when damaged, and in other environments that degrade the oxide layer faster than it can repair itself. Low-oxygen environments include stagnant water, water pooling in small gaps in the assembly, other problem environments include exposure to strong acids, and very high temperatures.
For the ARE, stainless steels should definitely be considered to be passive unless you're dealing with a scenario where the steel is exposed to clearly stagnant water, or is bolted together rather than welded in a generally wet environment - both of these situations would put the stainless steel at risk of becoming activated.
Best,
Ralph, the Amber Book Team
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